[iOS] Weaken DCHECKs in omnibox popup.

When the app is starting and focusing the omnibox at the same time,
the layout guides for the popup might not be constrained yet. It does
not cause any issues if they are constrained later.

Bug: 1112760
Change-Id: I9235ca681f18ea5b1c7882c955c1ffa28b533ed3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2410132
Auto-Submit: Stepan Khapugin <stkhapugin@chromium.org>
Reviewed-by: Robbie Gibson <rkgibson@google.com>
Commit-Queue: Robbie Gibson <rkgibson@google.com>
Cr-Commit-Position: refs/heads/master@{#807056}

ios/chrome/browser/ui/omnibox/popup/omnibox_popup_row_cell.mm

@@ -264,8 +264,8 @@ NSString* const kOmniboxPopupRowSwitchTabAccessibilityIdentifier =
                                                      view:self];
 
   // Layout guides should both be setup
-  DCHECK(imageLayoutGuide.isConstrained);
-  DCHECK(textLayoutGuide.isConstrained);
+  DCHECK(imageLayoutGuide);
+  DCHECK(textLayoutGuide);
 
   // The text stack view is attached to both ends of the layout gude. This is
   // because it needs to switch directions if the device is in LTR mode and the